1. Field of the Invention
This invention relates to an improvement in a wheel cap fitted to a wheel disk of an automobile or the like, and particularly to a wheel cap which can be fitted to a wheel disk easily and appropriately.
2. Description of the Prior Art
Recently, the demand for decreasing the weight of an automobile has been increased, and resin-made wheel caps have come to be used in place of metal-made ones. As a resin-made wheel cap, there is known a wheel cap which has a plurality of engaging parts disposed on the same circumference of circle on the back side of the wheel cap and a wire-type ring holder for urging the engaging parts in the radially outward direction for pressing them against the wheel disk, thereby engaging the wheel cap to the wheel disk. FIG. 17 shows a plan view of a conventional wheel cap with a ring holder, and FIG. 18 shows a cross-sectional view of an essential part of the cross-section in the normal condition wherein the wheel cap is fitted to a wheel disk. As shown in the figures, in the conventional wheel cap, an engaging part 2' projected from a base part 1' has a projection part 21' oscillated through appropriate elastic deformation, and is pressed against the wheel disk 6 by being urged in the radially outward direction by the ring holder 5'. The engaging part needs to be firmly fixed to the wheel disk and needs to have appropriate stiffness. For this purpose, the engaging part 2' is increased in general material thickness as shown in FIG. 18, or is provided with an appropriate reinforcing rib 22 as shown in FIG. 19. Accordingly, this type of conventional wheel cap can not necessarily be fitted easily, and the product weight thereof is relatively large.
When fitting such a wheel cap to a wheel disk, the part near a valve hole of the cap is first fitted to the wheel disk, and the opposite side is knocked-in later; therefore, the engaging part on the knocked side is greatly deformed, and the deformation is not recovered, resulting in that the wheel cap is fitted in an eccentric state and is liable to slip off. Also, after fitting, some of the engaging parts are similarly deformed greatly when an impact load is exerted thereon during running of the vehicle, leading to the trouble that the wheel cap becomes liable to slip off.
As a wheel cap free from the above-mentioned problems, there is known one which does not have the ring holder, as shown in FIG. 20 (Japanese Utility Model Application Laid-Open No. 57-10901(1982)). This wheel cap is characterized in that a clip 7 is provided on the inside surface thereof and a projected part 8 is provided in the direction of the inner peripheral surface thereof independently from the clip 7 so as to make contact with the inner peripheral surface of the wheel disk. Since deformation of the clip 7 is prevented by the contact of the projected part 8 with the wheel disk, this wheel cap is prevented from being fitted in an eccentric state. The wheel cap, however, has the problem that the shapes of the clip 7 and the peripheral part thereof are complicated, and it is generally difficult to produce the wheel cap (particularly, as one body) accurately and easily.
There is also known a wheel cap with a ring holder (A) which has an annular overall configuration and is provided with a plurality of stepped projected parts (a) bent in the direction of the outer periphery, as shown (in half) in FIG. 21, and a wheel cap with a ring holder (B) which is provided with projected parts (b) curved in the direction of the outer periphery, as shown in FIG. 22. In the former ring holder (A), the engaging part (not shown) of a base part (not shown) is urged in the radially outward direction by the projected parts (a). In the latter ring holder (B), the projected parts (b) themselve serve also as the engaging part. The ring holder (A) has a problem in workability such as dimensional accuracy because of its complicated shape. On the other hand, the ring holder (B) has the problem that it is poor in flexibility and can not be fitted to the base part easily.